1. Field of the Invention
This invention relates to a method of controlling individual cylinder fuel injection quantities in an electronically controlled diesel engine and a device therefor, particularly suitable for use in a motor vehicle, wherein rpm variations with every explosion cylinder are detected and a fuel injection quantity spill control actuator is controlled with every cylinder so as to eliminate a dispersion in rpm variation between the cylinders, so that engine vibrations due to the dispersion in fuel injection quantity between the cylinders can be reduced.
2. Description of the Prior Art
In general, the vibrations of a diesel engine during idling are by far higher than those of a gasoline engine. The diesel engine resiliently supported by an engine mounting mechanism resonates with the engine vibrations not only causing discomfort to occupants of a vehicle, but also adversely affecting components around the engine. This is mainly caused by the vibrations of the primary/secondary low frequencies attributed to periodical dispersions of the fuel fed under pressure to the respective cylinders at a rate only half the rpm of the diesel engine when the diesel engine is of four cycle type, for example. More specifically, in a diesel engine, if a dispersion occurs in the fuel injection quantity between the cylinders, then, as shown in FIG. 1, the rpm variations NE between the explosion cylinders (at 180.degree. CA (crank angle) in the case of a four cylinder engine) are not equal to one another, whereby surging S of deviations about a crank occurs at a cycle of every four explosions, which surge gives an uncomfortable feeling to an occupant of a vehicle. In the drawing, TDC designates top dead center.
It is conceivable to manufacture an engine body, a fuel injection pump, and an injection nozzle with very high accuracies, so that a dispersion in fuel quantities fed to respective cylinders can be reduced. However, to achieve this, great difficulties in production engineering are encountered, and a fuel injection pump and the like become very expensive. Alternatively, an engine mounting mechanism can be improved so as to reduce the vibrations of the engine. However, the mounting mechanism becomes complicated and expensive, and the vibrations of the diesel engine itself are not reduced thereby, thus not solving the fundamental problem.
To obviate the above-described problem, it is known to obtain an NE raw waveform by a gear 20 secured to a drive shaft 14 of a fuel injection pump 12 and an engine rotation sensor 22 mounted to a pump housing 12A as shown in FIG. 2, for example. An engine speed NE.sub.i (i=1 to 4) is calculated for each increment of 45.degree. CA in the 180.degree. of crank angle immediately before TDC of the cylinder to be corrected from the time duration .DELTA.T needed for the rotation through 22.5.degree. PA (pump angle) of the drive shaft 14 (corresponding to 45.degree. CA of the engine), which is detected by a fall of an NE pulse formed from the NE raw waveform as shown in FIG. 3.
An rpm variation DNE.sub.p (p=1 to 4) of every explosion cylinder is detected from the engine speed NE.sub.i as shown in FIG. 4, and the resultant value is compared with a mean value ##EQU1## of the rpm variations of all of the cylinders. When the rpm variation of the cylinder is smaller than the mean value WNDLT, the fuel injection quantity of the cylinder is considered to be too small; a fuel injection quantity .DELTA.q to be increased is learned in accordance with a difference DDNE.sub.p (p=1 to 4), as shown in FIG. 5, for example, and is implemented at the time of a subsequent fuel injection of the cylinder. On the contrary, when the rpm variation of the cylinder is larger than the mean value WNDLT, it is desirable to decrease the fuel injection quantity of the cylinder.
A fuel injection control actuator, such as a spill actuator for controlling a spill ring in a distribution type fuel injection pump, is readjusted for every cylinder until the rpm variations of the respective cylinders become uniform, as illustrated in FIG. 6, for example. The fuel injection quantity is increased or decreased with every cylinder to eliminate dispersion in fuel injection quantity between the cylinders, thereby reducing the engine vibrations.
Referring to FIG. 6, .DELTA.Q.sub.p (p =1 to 4) is an individual cylinder correction quantity as being an integrated value of every correction quantity .DELTA.q; K.sub.5 is a coefficient of correction for preventing hunting when the engine speed is within a range between 1000 rpm and 1500 rpm and the transmission is in neutral, wherein the higher the engine speed, the lower is the individual cylinder correction quantity; Q.sub.fin is an injection quantity calculated from a mean engine speed NE, an accelerator opening Accp and the like; and Vsp is an output from a spill position sensor for detecting a displacement of the spill control actuator.
Heretofore, in the distribution type fuel injection pump, for example, a delay of the spill ring in response and reach has been anticipated and the individual cylinder correction quantity has been previously outputted before a predetermined crank angle determined by an NE pulse so as not to interfere with the injections of other cylinders, whereby the individual cylinder control has been performed. However, there has been a possibility that the movement of the spill ring will come too late for the fuel injection of the cylinder to be corrected. For example, in order to make the calculated engine speed NE.sub.i, which has been obtained through every 45.degree. CA, approach a value as close as possible to the actual engine speed, it is necessary to bring the TDC to the center of a time period needed for the 45.degree. CA rotation used in the calculation of the engine speed, NE.sub.l, for example. Since the engine speed NE.sub.l is calculated from a time period between a time .DELTA..sub.1 and a time .DELTA..sub.2 as shown in FIG. 7, a great difference occurs in 45.degree. CA NE.sub.i depending upon whether the TDC position occurs midway between the time .DELTA..sub.1 and the time .DELTA..sub.2 as indicated by a solid line A or TDC occurs at the time .DELTA..sub.2 ' as indicated by a broken line B.
Since the individual cylinder correction quantity is determined from the rpm variation, in the individual cylinder fuel injection quantity control it is desirable that the waveform of NE.sub.i be one indicated by the solid line A. In consequence, TDC should occur 22.5.degree. CA before the calculation of NE.sub.l, i.e. the time .DELTA..sub.2. On the other hand, since the beginning of the fuel injection during idling and the like is normally located at a position around the TDC, there has been a high possibility that the spill ring cannot make a follow-up because, as against a time duration of 30 to 40 milliseconds (144.degree. CA to 192.degree. CA at 800 rpm) needed for the spill ring to move to a target value, in the conventional individual cylinder injection quantity correction, the command instructing a movement value to the spill ring actuator is given at the time of calculation of NE.sub.l, namely, 157.5.degree. CA before the injection. Particularly, the delay in reach becomes very large when an air conditioner is on, the engine is idling fast, and the like.